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need timing help- LZ24 engine.


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Basic info:

Z24 bottom end

U67 head

46mm twin SU's

Mercedes timing chain

was running fine, until a valve got stuck.

I did not build this engine- the PO did, and I'll be trying to reach out to him shortly ("Greybeard" on here)


Some of you may remember this problem with a stuck valve a few months back.


I finally got around to working on this. Put the motor at TDC (I later discovered I was at the exhaust end of the stroke- lobes on cyl #1 pointing up, like 10 & 2) pulled the head, and low and behold...there was a BOLT stuck between the valve. How it got there, or where it came from, I don't know. To top it off, it's a SAE bolt, so there is no home for it either.


Anyway, pulled the bolt out, valve popped back in, we can move on.


The old HG appeared to be a standard L-series HG. I compared it to a new Fel-Pro gasket, and the passages matched the old HG. So, I decided to use this.


I was hoping this wasn't going to be so involved. Having never done this before, and not being a straightforward engine, I prayed things would go back together as they came apart.


Well, with my inexperience comes mishaps. I didn't jam the chain tool down far enough, so when the cam sprocket came off during assembly (I was careful to mark the chain and sprocket somewhere to make sure it goes back the same way) The tensioner gave way and popped out. I discovered this when I tried to put the sprocket back on and there wasn't enough slack in the chain. Although I never did this procedure before, I figured that was the cause. No way around it, I proceeded to disassemble. Now at this point, the new HG was already on, and head bolts torqued to 60 ft-lb in proper order. So I didn't want to remove it again and decided to leave that alone. Instead, I proceeded to drain the coolant completely, remove radiator, distributor, water pump, crank bolt (that was an interesting episode, but it came off) oil pump, alt, and timing cover. I got a new timing gasket set and installed that.


Now here's where it got tricky for me. I watched Hainz's L-motor videos, read both 510 and 720 Haynes manuals, and although I have a basic concept of how the timing works, I can't get a grasp on how things are supposed to line up. I have the pulley pointed at the 0 on the timing cover. The woodruff key for the crank pulley is pointed straight up, and the timing mark on the crank gear (for the chain) is at the 3 o' clock position as it says in the 720 manual. For the cam sprocket, nothing lines up to anything when it's on compression stroke. When it's lined up to how I disassembled it (the exhaust stroke) the "groove" on the sprocket lines up somewhat to the timing notch on the thrust plate. There are no markings on the chain, as it's a Mercedes chain so no bright links, orange dots or anything to help with timing. When I pulled the oil pump, it was 180 out from the marks, which is another way I figured out that I was on the opposite end of the stroke. Since I reassembled the motor the same way, I reinstalled the oil pump in this same position, which gives me the 11:28 position on the distributor side, but 180 out.


I put it back together this morning to see if it would start.


It started after a while (carbs emptied out when I removed them) but it runs like poo. On the other hand, it idles, not very well but it keeps running. Input on the gas pedal doesn't do much. A slight change in revs, but not much else. I am quite sure something went wrong with timing when I reassembled everything. I did shut it down quickly because I didn't reinstall the radiator yet, figuring that I'd have to disassemble it again.


So here I am guys, and I need a bit of help. I want to time this right, and want to do this so I can gain some knowledge on this stuff. Can anyone give me some specifics? What am I doing wrong? And how do I start from scratch on the timing? I'd rather not take it apart again, but I will if I have to...


If you need specific pics, let me know and I'll take them and post up!


Overall, it's not the best experience but I already learned quite a bit on how all this works- if I can get it working well, now that would be a treat.

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Head timing at TDC (0 degrees)...should look like this...


Position of the grooves/notches.






And yes...pics are a given


Or.....If your TC cover was removed you could check....

L20B...22 sections/44 links

LZ24 would be an extra 2 sections/4 links... total



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Sealik, thanks for the input.

*edit* just noticed the pic of the chain links- this is very helpful, thank you!!


Here are my pics.


After a bit more studying I may have been confused as to where TDC was.

If the lobes at cyl 1 are pointing up 10 and 2, then it seems as this is when settings should happen? (according to Hainz's video)


Anyhow, here's where I'm at, I set everything to this point. I also removed the oil pump and lined it up, instead of being out 180 like in my first post.


Now, the truck won't start, but in theory, this should be all correct. But please correct me if I am not!


crank pulley. v-notch on the pulley (orange) at 0 on the marker.



cam sprocket position.



v-notch on pulley in relation to timing mark on thrust plate. The notch is about 1/2 way out from the timing mark.



position of cam.



distributor shaft position.



charging battery now...it went flat from trying to start it. I guess it's a good thing the truck isn't a required driver, but it's blocking my 510 in, and at this point, I can't drive either one :rofl:

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If I an seeing this correctly the groove in the cam sprocket is to the right of the horizontal line on the thrust plate??? Correct?


If so, you have the cam timing slightly advanced from optimal. An advanced cam favors low RPM cylinder filling but is detrimental to high RPM power. It should run great at start and idle this way. It could be moved back one number on the sprocket, which would retard it about 4 degrees and put the groove directly under the line, but like I said it should run fine like this.


In ALL cases... If an L/Z motor is at TDC on the compression stroke, it matters not where the chain bright links are, or how many links you added, or how much you have shaved off your head or what sprocket number you are on. What matters is that the groove in the sprocket is directly below the line on the thrust plate OR just slightly to the right of it. No matter what else.... the cam will then be properly timed to the crankshaft.

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If I an seeing this correctly the groove in the cam sprocket is to the right of the horizontal line on the thrust plate??? Correct?


Yeah...hard to tell from pic....but...I also noticed....It looks like he's a little past TDC at the crank?

Not sure if that would account for that difference though.


When setting TDC...rotate engine CW.....do not go past 0 degrees and then back the engine up to TDC

If you do go past....rotate engine CCW.....lets say to 15 degrees BTDC and try again

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Hmmm....make 100% sure that the TDC mark (zero) on your pulley and cover actually do correspond to the #1 piston being at TDC (use a strong flashlight to peer into the plug hole or use a small wooden dowel touching the piston top as you rock the crank a few degrees either way, feeling for TDC).

Also, as that valve was being held open by the orphan SAE bolt (!!), are you certain the valve face and seat are still concentric and sealing well? Just a wonder since a bent valve would be easy to imagine here.

Good luck,


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Thanks guys, this is all very helpful.


When I had the head off, 0 on the crank pulley and cover lead to the #1 piston at TDC. So I know that's where it should be.

Just for my knowledge, should 0 on the crank pulley equal TDC? And is this where I should be setting everything? Cam sprocket groove, and distributor shaft at 11:28 position?


Datzenmike, the groove on the cam sprocket is just forward of the thrust plate line. So the groove is halfway on the line. The other half is right of it.


Ray, the valve and face looked good. If anything the bolt was much softer than both so it took the brunt of any possible damage. In any case, it still started and ran somewhat before I pulled it all apart, SAE bolt and all! So whatever is causing it to not run at the moment is purely my error and lack of knowledge. I know the engine runs, I know it's all there, just a matter of getting everything where it should be at the right time.


I'm going to go back out there and give it another shot later today. Thanks for all the great info!

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Datzenmike, the groove on the cam sprocket is just forward of the thrust plate line. So the groove is halfway on the line. The other half is right of it.



That is absolutely perfect cam timing.


If running rough it's likely carb sediment stirred up from having the head off. Primary jet has some trash in it.

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Was the motor running good with the SUs prior?....Set up correctly?

Chokes engaged at start up....?.......might help, give it a richer mixture

Jet screws should be about 2 turns out to start out with....all relative to needles

Specs on your motor/head/cam?....


Curious about what needles you are running....when you get a chance, could you have a look?..... :)

I've got an LZ23/46mm SUs in a 510....lots of fun :w00t:

I'm running RAs....just a tad rich at idle....better than the N27s though, much too lean



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The motor ran fine before my incident. Don't have any specs, as I didn't build the motor, but hopefully the PO can shed some light on it. I am not sure of the needles, but when all is said and running, I'll be happy to dive into the carbs and give them a proper clean and tune, and figure out just what's in them!


I have news!


After staring at the engine for a while, I found something that slipped my attention.

If you recall, originally the dizzy shaft was out 180. Why this was the case, I'm not sure but I think I may have found the reason why.

When I looked at the rotor, after I adjusted everything, and installed the oil pump shaft correctly, the plug wires were still out 180.

I located #1 on the diz, redid the wires (the routing is really bad in this setup, which may explain the 180 by the PO) threw the valve cover back on, cranked the key and BOOM! Engine jumped to life on the first crank. :thumbup: And there is good response.


BUT...there is a horrible noise from the engine. Sounds like it could be valves smacking the piston.

I suspect timing is still off...should I try and 0 everything out again- including the advance on the cam?

OR...maybe that valve that caused this whole fiasco is bent after all?


As a pain in the ass as this is, and although I am still not out of the woods yet, this has been incredibly educational. I have such a better understanding of how all this works, and although it's making a racket, there was some great satisfaction in hearing that thing come to life this evening.

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Timing off a little won't cause the pistons to touch the valves (with a stock engine). But if the valve is bent this can happen.


To test the valve, when you have the head off, rotate the cam so that valve is completely closed, set the head upside down, fill the chamber with water and verify it hold for 5 minutes. If the water runs right out, then the valve is bent or the valve face or valve seat is damaged.

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John, it was great to catch up with you. And thanks for all that great info- I probably should have called ya before I started working on this!


So the noise coming from the engine is presumably caused by me installing the incorrect HG. Bore on the L20 HG isn't matching the bore of the block. I need either a Nissan comp HG, or a combo of a Z24 HG with the timing section of the L20 HG.


I'll be ordering the Z24HG today, and I'll cut off the timing part of the L20 HG I have in there now.


And the oil pump was 180 out for what I guessed, routing of the plug wires. I might go back to this because the wires now are less than ideal.


Thanks for the tip of the retarded cam as well!


I have a nice holiday starting tomorrow for the 4th, so I'll be tearing into things this week again. I do feel good about this, now that I'm armed with this info.

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I figured- should I just stack the L20 HG and Z24 HG to compare the openings, and add the L20 holes to it?


Not that easy......I believe there is another thread on the number of holes needed...location



Z24 Block



L head




L Block




Z22 Block/Z24 HG....LZ23. 9 holes in HG/ 7 in block




L HG on top

Z24 HG on bottom....after I fucked it up... :D


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Just wanted to report that I replaced the HG with a proper Z24, slightly modded to match the Nissan Comp gasket that was on there originally.

I didn't replace the timing cover section with the L HG part, but modified it to match up the different mounting holes for the timing cover. (Found this info on a Ratsun thread) It much easier this way.


Retarded the timing 1 tooth on the cam, as advised by Graybeard.


Tightened everything up, left the plug wires and oil pump as is for now. Crossed my fingers and cranked it.



The sound of a nicely running LZ24!


I let it run for just a moment, then shut it down and reinstalled the radiator and related plumbing. Filled it up, topped off the oil (lost some throughout this ordeal) and let it warm up. Looked good- then I let it run through some RPM ranges.


Shut the hood and drove it a few miles. I had forgotten how nice this engine pulls, even though the SU's could use a clean and tune. Got home, checked everything out. No leaks, no drama, just a nice running motor.


Next step would be to dive into the SU's but I'm going to leave it as is for now...I need to get back to my regular scheduled programming!


It's been a hell of a few weeks but the experience has been rewarding. I feel like I could build a L-motor now, which I am now tempted to do for my 510.


Thanks guys for all of your help, couldn't have done it without your valuable input! :thumbup:

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Crazy shit...


...."BUT...there is a horrible noise from the engine. Sounds like it could be valves smacking the piston"....


Can't wrap my head around that sound from just using the smaller l20 HG....if anything... it would just blow out , and..... possibly sound like the aforementioned??



Condition of HG on removal....?...Pics of new/modified HG???

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The L HG looked fine when I removed it, but you could see where the pistons were making contact. They were hitting the metal rings around the holes, and that's where the metallic smacking sound was coming from. It didn't blow out at all.


No contact on the pistons and valves, so all was good.


Unfortunately I was working fast and didn't have the insight to take a pic of the modded Z24 gasket. It was only a few small holes to match the Nissan Comp gasket, and even at that, I don't think they do much? There's a LZ22 build thread on here that I also used for reference.


In any case, now it matches what was in there, and if it lasted 15 or so years since when John built the motor, I'd say it's good to go for a while.

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Glad all turned out well and it's running again.


An 85mm L20B gasket would protrude about 2mm over the edge of the Z24 cylinder all the way around. The Z24 piston stops 0.45mm below the top of the block. By the numbers it shouldn't touch...


That's true Mike, but when the gasket compresses, the head, with the smaller L-20 combustion chamber will push the gasket with the smaller bore

down into the cylinder as it compresses when the head is torqued down.


I suppose the combustion chamber on the L-20 head really should be opened up to the proper bore size for the block...

If I ever build another 2.4 i'll go that route.



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